Micro/nanowires with integrated ohmic contacts have been prepared from bulk wafers by metal deposition and patterning, high-temperature annealing, and anisotropic chemical etching. Now, electrical devices, formed with high-quality single-crystalline seminconductor nano- and microstructures on large area mechanically flexible plastic substrates, which are of great interest for a wide range of applications in displays, sensors, medical devices and other systems. A number of approaches have been demonstrated to transfer high-quality semiconductor materials onto plastic substrates.
Traditional photolithography methods, although they are versatile in the architectures and compositions of surface features to be formed, are costly and require specialized equipment. Beyond this, photolithography methods have difficulty patterning very large and/or non-rigid surfaces such as textiles, paper, plastics, and the like.
In laser supported etching methods the laser beam scans the entire etch pattern point for point on the substrate, which, in addition to a high degree of precision, also requires considerable adjustment effort and is very time-consuming.
But meanwhile it is possible to provide high performance devices that can be built directly on a wide range of unusual device substrates, such as plastic or paper. In particular, transfer printing organized arrays of such wires at low temperatures onto plastic substrates yield high-quality bendable metal-semiconductor field-effect transistors; for example electrical devices are prepared on poly(ethylene terephthalate) [PET] {Y. Sun et al.; Applied Physics Letters, 87, 083501 (2005)}. This latter approach uses high quality bulk GaAs wafers as starting material, “topdown” fabrication procedures to form the micro/nanowires and transfer printing techniques that use elastomeric stamps to integrate well ordered arrays of these wires with plastic substrates. In this process, pattern of photoresist lines is defined on top of the metal stripes. The openings lie between adjacent metal stripes and openings allow the etchant to diffuse to GaAs surface to etch GaAs anisotropically. The anisotropic etching generated reverse mesas and undercuts along the surface of GaAs, resulting in the fabrication of GaAs wires released from the mother wafer.
This means, methods of patterning surfaces are well known and include photolithography techniques, as well as the soft contact printing techniques such as “micro-contact printing” as also disclosed in U.S. Pat. No. 5,512,131.
With soft-lithography techniques surface features may be produced having lateral dimensions as small as 40 nm, but the range of surface features that can be formed using these techniques is limited.
This means according to the current state of the art, any desired structures can be etched selectively in a polymer based substrates, directly by laser-supported etching methods or, after masking by wet-chemical methods or by dry-etching methods.
In another approach pastes are used to form a variety of surface features having complex architecture. Typically, pastes are applied to surfaces by screen printing, spraying, ink-jet printing, or syringe deposition. However, the lateral dimensions of surface features produced by these methods are also limited. Especially, it has been found difficult to achieve lateral dimensions below 100 μm. Especially, if the surface, which has to be patterned or structured, is composed of different materials and is not even, it is difficult to pattern selectively the polymer material uniformly and homogeneously.
The wet-chemical and dry etching methods include material-intensive, time-consuming and expensive process steps:
A. Masking of the areas not to be etched, for example by                photolithography: production of a negative or positive of the etch structure                    (depending on the resist), drying of the photo-resist, exposure of the coated            substrate surface, development, rinsing, if desired drying                        
B. Etching of the structures by:                dipping methods (for example wet etching in wet-chemical banks): dipping of                    the substrates into the etch bath, etching process, repeated rinsing in H2O            cascade basins, drying                        spin-on or spray methods: the etching solution is applied to a rotating substrate, the etching operation can take place without/with input of energy                    (for example IR or UV irradiation), and this is followed by rinsing and drying                        dry-etching methods, such as, for example, plasma etching in expensive                    vacuum units or etching with reactive gases in flow reactors                        
As already mentioned above, the disadvantages of these etching methods described are due to the time-consuming, material-intensive, expensive process steps which are in some cases complex from a technologically or safety point of view or are carried out batch-wise.